194 The Gold and Placer Mines of Wicklow. [April, 
the ravine consists of — above meteoric drift, under which is 
water-formed drift, and at the base of the latter in places is 
the auriferous or “ black sand.” The black sand is found in 
“runs ” or lines, and these occur in channels or slight hollows 
that have been denuded or worn out along nearly parallel 
lines of dislocation, or master-joints, in the underlying 
Cambro- Silurian rocks. The miners know when they are 
coming to a “ run,” as the lamination of the “ bottom rock” 
is “crumpled,” as the twisting and breaking-up of the rock 
adjoining the fault or dislocation lines is locally called. In 
each sedtion of the valley these breaks have general bearings, 
so that when the direction of one run is known all others are 
nearly parallel. One set of parallel breaks may, however, be 
crossed by another, and at the junction of the two systems 
the channels are deeper, and consequently in such spot more 
gold collects than elsewhere ; so that on a map of a placer 
the rich spots occur somewhat like the corners of the squares 
on a chess-board, only more oblique to one another. 
In the Red Holes Mine the surface of the “ bottom rock” 
in general is ground smooth, as if a rapid torrent had ran 
over it for years. In the overlying water-drift all the rock 
fragments are abraded, and rarely — even on the Gabbro, 
quartz, and other hard rocks — was a trace of ice-work 
detected ; but a few ice-dressed fragments do occur in the 
higher meteoric drift. It would appear that when the ice 
was melting off the Wicklow hills great torrents were flowing 
down the different ravines, and when the ice had all melted 
and the water-supply was gone the torrents dried up, while 
subsequently the marginal cliffs of the ravines weathered 
into slopes, their detritus forming the meteoric drift now 
found above the water-drift. 
All the modern mines in the neighbourhood of Croghan 
Kinshella are “ shallow placers,” the deepest being less than 
30 feet, while no deep trials have been made. In nearly all 
other gold regions the precious metal has been worked not 
only in shallow but also in “ deep placers,” and, if we may 
reason from analogy, it appears probable that there are vast 
supplies of unknown auriferous sands under the deep river 
and estuary accumulations in the flats at Wooden Bridge, and 
other places in the valleys of the Ovoca and its tributaries. 
